This invention relates generally to methods and apparatus for logging earth boreholes and specifically to methods and apparatus utilizing self-contained well logging instruments in earth boreholes.
It has become relatively common within the last few years to drill wells in the search for oil and gas and the like with a portion of the bore deviating from the usual vertical orientation thereof. The deviation of inclination may extend for a considerable distance at angles ranging to 70.degree., sometimes returning to the usual vertical orientation. In some instances, such boreholes may even extend past 90.degree. from the vertical and actually be extending in the "up" direction for some distance.
It is also well known in the art of drilling such wells to attempt the logging of the formations surrounding such boreholes with logging instruments run into the well bore on a wireline and/or cable to perform various operations. Such tools usually depend upon the force of gravity to permit positioning of the well tools at the desired formation in the well bore.
Manifestly, the relatively horizontal angle of the deviated portion of the well bore will not permit the wireline-actuated tools to move into the lower portion of the well bore since friction of the well tool in the deviated portion works against the force of gravity. Thus, it has become essential to provide some means of causing the well logging instrument to pass through the deviated portions of the well bore.
Another problem associated with such boreholes relates to the instability of some formations penetrated by the well bore, thus causing borehole diameter changes, some very abrupt. Ledges are formed and the logging instrument lodges against them.
Furthermore, although there have been attempts in the prior art to pump logging instruments down the borehole, such instruments have generally suffered from the problems associated with having a wireline attached to the instrument, or because of having no correlation between the well logging signals and the true depth in the borehole.
It is therefore the primary object of the present invention to provide a new and improved method and apparatus for logging earth boreholes;
It is also an object of the present invention to provide new and improved method and apparatus for logging deviated boreholes requiring no wireline from the earth's surface;
It is yet another object of the present invention to provide new and improved method and apparatus for logging earth boreholes and for correlating the logging data with the true depth in the borehole.
The objects of the invention are accomplished, generally, by apparatus having means to measure the acceleration of the apparatus while traversing an earth borehole, means to convert such acceleration to indications of depth in the borehole, means for providing indications of characteristics of the earth formations surrounding the borehole, and means to correlate said depth indications with said indications of the characteristics of the earth formations, and by methods relating thereto.